I believe luke.pearson@mongodb.com already looked at this as part of the initial modularity push, but enough has changed with disagg that I think this is worth re-litigating.

The interface for the block manager has ended up in the block cache directory, which is fairly confusing. This comes from the design of having the block cache sit "in front of" the block manager, rather than being something "internal to" the block manager.

This design is not inherently bad – it allows the block cache to function regardless of which type of block manager is used, which has already proven useful in disagg. But that doesn't mean the interface has to live in the block cache directory, and I suspect with a little more work we can move the interface somewhere more appropriate.